Stator assemblies having a multi-phase winding wound about a stator core are well known in the art. For example, in a three phase motor or generator each phase may have one or more groups of coils, and each group may overlap another group. In such an arrangement, windings for different phases are wound through a plurality of slots formed in the stator core to form coils of different phase. The portions of the coils extending from one slot to another along the ends of the stator core form the end turns. In such multi-phase stators, the end turns of the coils of different phases are typically located adjacent to one another. Thus, when the coils are electrically energized, potential differences are developed between the end turns of the coils of different phases. It is, therefore, normal practice to provide an insulating barrier between adjacent end turns of the coils of different phases.
One type of insulating barrier commonly used in the art is an electrically insulating composite paper. This composite paper typically comprises layers of Aramid and Mylar materials in varying thicknesses, depending on the physical and electrical requirements of any given application.
However, in electrical machines heat tends to be generated through, amongst other things, resistance in the coils. The machine rating is often determined by the actual temperature rise of the machine, and thus the cooling efficiency of the construction may help to determine the rating of the machine.
A problem which has been identified in machines which use composite insulating paper between groups of coils is that the composite insulating paper may reduce the cooling efficiency of the machine. This is firstly because the exposed surface area of the coils may be reduced, and secondly because air flow through the coils may be restricted. Moreover, during the manufacturing process, the composite insulating paper may become damaged and/or dislodged.
While recent attempts have been made to increase cooling efficiency, there is still a need for an apparatus that can electrically insulate coils of different phases while affording adequate cooling. This goal is further complicated by the fact that rigidity and compactness of the stator assembly (including the end coils) is desirable during manufacturing to prevent damage to the coils.